1.6%, Not 97%, Agree that Humans are the Main Cause of Global Warming

Mark Bahner, a commenter on my previous post on global warming and on David Friedman's post, has sifted through the data behind John Cook's statement that 97% of climate scientists who stated a position believe that humans are the main cause of global warming. Recall that Bedford and Cook lumped together those who believe that humans are the main cause with those who believe that humans are a cause. Cook et al did not report the percent of abstracts in which the scientists said that humans are the main cause of global warming. But Bedford and Cook (the same Cook), citing Cook et al, misrepresented the results of Cook et al.

Unfortunately, neither Cook et al nor Bedford and Cook reported, even though they had a category for, the percent of abstracts that claimed that humans are the main cause of global warming. Fortunately, Mark Bahner, an enterprising commenter on both David Friedman's and my posts, managed to find their data and went through and did his own calculation. He reported his results in a comment on my previous post but, because the post was two days ago, it's worth pointing out in a separate post. Thus this one.

According to Bahner (and I have not gone through and checked the raw data for myself), of the 11,944 abstracts that Cook et al examined, only 64 claimed explicitly that humans are the main cause of global warming.

Here are the categories that Cook et al state. I have added the numbers that Bahner found beside each.

So 64 out of 11,944, or 0.5%, take the view that humans are the main cause of global warming. But that includes all abstracts, including those that did not take a position. It would be nice to take the 64 as a percent of those that did take a position. Unfortunately, in their data set, Cook et al put 4a, those that do not address the cause of global warming, with 4b, those that express the view that humans' role in global warming is uncertain or undefined. It would be nice to separate them, but we can't unless we have the even rawer data. So let's generously conclude that everyone in category 4 has expressed no view. That's a total of 7970, leaving a total of 3,974 that have expressed a view. The 64 who think the main cause is humans is, drum roll please: 1.6%.

1.6% is pretty different from 97%.

UPDATE: Commenter Dana Nuccitelli writes below: "This argument is wrong and has been debunked several times, i.e. here and here." But go to the articles and read them and you will see that the articles do not debunk my argument. Indeed, that would be difficult to do since my argument is based on Cook's own data.

The problem is that there is rampant confusion about what kind of a consensus there is.

There is a 97%+ consensus that a doubling of CO2 produces an additional ~3.4 Watts/Meter Squared which, all things being equal, results in around a 1 degree C warming.

So, there is consensus that man causes some warming.

But there is no consensus regarding how much. In fact, there is a raging debate going on about it. Specifically about the sign and magnitude of climate feedbacks and therefore whether there is a significant problem or not.

"It's hard to believe perceptions of a consensus on a serious climate change problem are completely fabricated by the media."

I don't know whether it is fabricated by the media or not, and if that is the claim then this claim does not seem very plausible to me either. However, it seems to me that all you need is a very vocal minority with a substantial stake or an honest belief in AGW to create the perception in the media that there exists such a consensus.

The point isn't that the consensus is completely fabricated by the media. I don't think David Henderson or David Friedman are denying that there is a broad consensus among climate scientists that anthropogenic global warming is a serious concern. What they're drawing attention to is a "debate" so plagued by rhetoric and politics that for it's tough for the outsider to trust any report, finding, or factoid we hear about global warming.

It's hard to learn about these numbers and not suspect the authors of willfully misleading the public with egregious spin. Perhaps they did it with the best intentions; maybe they believe the dangers anthropogenic global warming so great that misleading the public is justified, especially if their opponents are already using such dishonest tactics. Whatever the reason, it's things like this which end up undermining any presupposition of authority in the eyes of less partisan observers.

In particular, stories like this undermine the oft-heard narrative of a community of objective and like-minded climate scientists vs. a handful of cranks funded by big oil. Far from only delegitimising the opposition, which appears to be the intent of the authors, they end up instead deligitimising everyone who partakes in the debate, including themselves.

Lee -
I'm not sure that was the intent of the authors. How do you know that? I'm guessing they weren't careful in making that claim about the study (or someone else wasn't - it's amazing how easily communications departments miscommunicate). The study seems careful enough from what everybody's been reporting. I don't know the guy - I don't feel comfortable making that sort of claim about him.

How much of the 3,832 that comprise the rest of the 97% think AGW is substantial enough to be worrisome?

This question is actually far more interesting and relevant than the question the researchers try to answer. For when the "97%" gets parroted outside of journals, this is the question that the "97%" implicitly accrues to because this is the question the public wants answered.

But this exercise measures no such thing. Even scientists who believe that climate change is real and that AGW is the main cause may not think that it is bad enough or that we understand it well enough to take policy action on it now. When these people submit scientific papers -- not economic papers or political papers, but scientific papers -- they will put their understanding of the consensus on the science in the abstract. Shocking, I know. There may even be some in the 1.6% who would resent being counted as calling for government action.

Another way to look at it is that there are three interesting divisions among climate scientists:

1. Those who believe that AGW is real and who believe government must take great measures to address it now.
2. Those who believe that AGW is real and who do not believe government must take great measures to address it now.
3. Those who do not believe in AGW.

Exercises such as Cook, et al.'s, are designed to count #2 with #1 against the crazy climate change deniers in #3 in order to push the agenda of #1. But #2 (I suspect) is far larger than #3, yet by construction does not want the agenda of #1.

Such counting of consensus is a disingenuous attempt to imply that only a crazy minority does not agree with leading climate change scientists, who of course advocate the consensus.

MikeP - not that anyone should turn to climate scientists for policy advice. But perhaps it's because I think that that I was comfortable with lumping them together from the beginning, although (1.) they should not be misleadingly defined, and (2.) it would be nice to know the variability within that 97%.

I'll be honest, in the previous post contesting the 97% assertion, I felt like I had been hoodwinked by the end of it (by Cook, not the "OP"). I appreciated the callout and am a fan of honesty in academics.

This post, however, seems to be a bit too far the other way. Using ONLY those who quantify seems like cherry picking (to me). Granted, Cook certainly did his own cherry picking, but let's not counter that with the same error.

...into Excel, run a "text-to-columns" and then "countif("1"), countif("2"), countif("3"), etc.

In fact, the very idea that Cook et al. combined the three groups "to simplify analysis" is laughable. A third-grader (who knows Excel...do they teach Excel by the third grade?) could what I did in about the same time...probably less than 10 minutes. A question I have is why Environmental Research Letters even published the paper with the combining of the first three categories? Why didn't the peer-reviewer(s) say, "You ought to present a table that breaks out all seven categories, then you can combine them at a later time"?

But let's get something straight: the paper is junk. Even more important, John Cook later misrepresented the paper's results. (As I commented on David Friedman's website, perhaps Mr. Cook has suffered a brain injury, and forgotten what his paper found. Until/unless we learn that's the case, I think David Friedman's conclusion that Mr. Cook deliberately misrepresented his paper's findings is the most logical conclusion.)

...BUT...that doesn't mean that there isn't a substantial amount of agreement that humans have caused most of the warming observed since 1950. Which renders the title of this blog post hilariously inaccurate hyperbole. (You really should put a "wink" after the headline, David. :-))

There is an interesting discussion of the Cook et al. "Consensus" paper on the National Climate Change Forum blog:

There, among climate scientists, the nuances were dealt with. A time frame was specified (150 years) and the degree of causation was quantified. For the sake of this discussion, let’s call “climate scientists” the ones who self-identify as specialists in climate science and actively publish to some extent in the climate science arena.

Is global warming happening? Absolutely! 98%-99%
Are we an important cause? Yes! 85%-93%
Are we “the” cause, as in is it mostly human? Yes. 75%"

So even though this paper is junk, and Mr. Cook has misrepresented his paper to boot, there are legitimate papers that say that the percentage agreeing that humans have caused most of the warming since ~1860 is well above 50%. (And certainly not only 1.6%!) (C'mon, David!)

there is a broad consensus among climate scientists that anthropogenic global warming is a serious concern

Speaking of egregious spin, I hope that's not what you are doing. You've made a logical leap, a non sequitur. There is no evidence for a "broad consensus" that agw is a "serious concern." There probably isn't anything like a consensus that it is a serious concern. That it exists as a phenomenon, sure, there's definitely such a "broad consensus." But it does not follow from the existence of a phenomenon and agreement on that, that an agreement exists that said phenomenon is a serious concern.

Here's an appropriate - although subject to shortcomings - way of calculating agreement.

You should only be using papers that have expressed a position on AGW as the main cause. So you should leave numbers 2,3, and 4 out of the calculation. I think it's reasonable to include 5 and 6 because minimizing/rejecting AGW precludes thinking it's the main cause.

This gives 64/(64+54+15+9)=64/132=48.5%.

Now, as others have mentioned, the question is whether those who wrote 2,3, and 4 would raise or lower that number. My guess is that 2 and 3 would considerably raise it, but I'm not sure on 4 (probably raise it but less so).

Since the above calculation is from a small sample it would presumably change quite a lot from more info, but it's safe to say that the average would definitely not be raised to 97%. Even just adding categories 2 and 3, that would require about 100% of the authors that wrote those papers to agree that AGW is the main cause.

As may or may not be clear, I wasn't making any claim about how many climate scientists believe that humans are the main cause of warming, let alone about whether it is true. My point was that the claim that Cook et. al. showed that 97% of the articles held that humans are the main cause was either blatantly dishonest or wildly mistaken. That claim was made explicitly by Cook and has been repeated by many other people. The correct claim, ignoring complications about how one treats category 4, is that the article showed that 1.6% of the articles endorsed that claim and that 97% endorsed or implied endorsement of at least the weaker claim that humans contribute to warming.

The reason all this matters is that practically everyone in the argument is dependent on second hand information, on claims from sources they trust about what the evidence is. Almost nobody has the expertise and time needed to evaluate any significant fraction of the evidence for himself. Different people trust different sources, with the result that different people have different confident beliefs about what the evidence is. If you are sure the evidence unambiguously supports your view, it's natural to interpret anyone who disagrees as a fool or a rogue—and if you watch the arguments, that's what routinely happens in both directions.

I believe I have demonstrated, by evidence that any reader can check for himself, that at least one important source on one side of the argument cannot be trusted, is not merely careless but blatantly dishonest. John Cook is not only the principal author of an article whose supposed result is widely repeated. He's also the administrator of a major web page supporting CAGW. The evidence I have offered shows, I think, that everything on the SkepticalScience web page ought to be viewed as possibly a lie until confirmed from some other source. And I hope it will persuade the small minority of supporters of CAGW who are intelligent, reasonable, open minded people that they should sharply lower their confidence in their beliefs in the subject, since at least some of their trusted sources shouldn't be.

I'm not, by the way, suggesting that the fraction of intelligent, reasonable, and open minded people on the other side of the argument is any higher. Participants in online discussions of this issue and probably most others, on both sides, are mostly cheering their team not trying to figure what's true.

2. How much of the 3,832 think it comprises the main but did not state it (they all sound like they failed to weigh in on the magnitude)?

If Mark is around maybe he has insights into the latter question. I imagine we need a climate scientist to answer the former.

Both numbers are substantial I imagine. It's hard to believe perceptions of a consensus on a serious climate change problem are completely fabricated by the media.

I don't see the point of speculating on this paper. It's just complete garbage. The difference between 4a and 4b is huge. They apparently checked 1000 abstracts to see which ones fell into 4a and which ones fell into 4b. But then they didn't even report their results (or include the result in their data file, which would have been simple to do).

Why not simply accept the AMS survey paper as a reasonable approximation of current thinking:

"Is global warming happening? Absolutely! 98%-99%
Are we an important cause? Yes! 85%-93%
Are we “the” cause, as in is it mostly human? Yes. 75%"

But that tells us essentially nothing about the more important questions:

1) What warming can we expect over the remainder of the 21st century?
2) What will be the world GDP, life expectancy, malaria death rates, etc. etc. *with* expected global warming if we do nothing...and if we do various things?

If the world per-capita GDP is $1,000,000+ (or even the much lower GDPs in *any* of the IPCC scenarios) then the people of the 22nd century can simply spend ~10% of their (much-higher-than-present) GDP for a few decades, to get the atmospheric CO2 concentration down to 350 ppm.

In other words, it will be a relatively trivial thing for them, since the U.S. spent about 10% of it's GDP on defense for many decades after WWII.

I've no ax to grind. There is plenty of evidence of a broad consensus among climate scientists that anthropogenic global warming is a serious concern. Indeed, Mark Bahner, who exposed Cook's misdeeds, acknowledges that such a consensus exists and even provides alternate evidence. Neither do David Henderson nor David Friedman mean to assert otherwise, because there really is a broad consensus. The argument is just that the 97% figure is wildly misleading, at best, and a bare-faced lie, at worst. The paper it's based on doesn't support that conclusion--it's trash.

Whether the actual consensus is right, and what it means for policy, are different issues, and I don't have especially strong opinions on the matter.

Also, don't accuse me of a non-sequitur unless you know what that means. Nowhere did I attempt to infer from a consensus on the existence of anthropogenic global warming to a consensus that it's a serious concern. No, I merely asserted that there is such a consensus, and it seems you need to somehow come to terms with that fact.

'I'm not sure that was the intent of the authors. How do you know that?'

Because it's the best explanation of the facts as I understand them. I could be wrong, of course, and I'm also uncomfortable saying this about the authors. The whole global warming "debate" makes me uncomfortable, because time and again we find ourselves in the position where it seems, for all the world, like we're being manipulated, mislead, and lied to. It's a nasty business--it's politics.

You write, "There is plenty of evidence of a broad consensus among climate scientists that anthropogenic global warming is a serious concern. Indeed, Mark Bahner, who exposed Cook's misdeeds, acknowledges that such a consensus exists and even provides alternate evidence."

Whoa! I provided no evidence that there is a "broad consensus among climate scientists that anthropogenic warming is a serious concern."

I provided evidence that there is a concensus that most of the warming of the last 150 years has been caused by humans. That's all.

And even if I had provided evidence that "climate scientists" think that "anthropogenic warming is a serious concern"...how would that even be a very important consideration? Of course people who study something as the focal point of their career are going to say that what they do is important.

You also write, "Nowhere did I attempt to infer from a consensus on the existence of anthropogenic global warming to a consensus that it's a serious concern."

??? You've got me completely baffled here. What about where you just wrote: "There is plenty of evidence of a broad consensus among climate scientists that anthropogenic global warming is a serious concern. Indeed, Mark Bahner, who exposed Cook's misdeeds, acknowledges that such a consensus exists and even provides alternate evidence."

> I provided evidence that there is a concensus that most of the warming of the last 150 years has been caused by humans. That's all.

That's like saying 'I provided evidence of the evidence'. If that's all evidence does then it's useless, because it's supposed to support or contradict theories, explanations, or hypotheses which, naturally, go beyond the evidence itself. Since a worldwide rise in temperatures is, uncontroversially, a serious concern, whatever its cause and whatever the appropriate response, then the very acknowledgment of such a phenomenon is prima facie evidence of serious concern. That is, unless we also must provide evidence that climate scientists are concerned about fragile ecosystems, rising sea levels, economic upheavals, and so on.

But claiming this to be a non-sequitur is to mistake an assumption for a conclusion. It's as though I said 'humans are omnivores' and was accused of a non-sequitur because I hadn't specified that humans are capable of digesting food and, therefore, evidence of a human preparing food is inadmissible as evidence that humans eat unless independent evidence is established that they can also digest food.

I don't really have any patience for these arguments, because such demands can be made indefinitely all in the guise of humble scepticism and empiricism, when it's really just a strategy to evade a good explanation of the facts.

> how would that even be a very important consideration?

It's not. Indeed, it's vague enough to be rather banal. I was responding Andrew_FL who appears, nonetheless, to be highly sceptical of this claim and think it appropriate to accuse me of a non-sequitur. When I'm trying to present a logical deduction from premisses to conclusion, then I'll make that clear, otherwise accusations of non-sequiturs are almost always misplaced.

We need to remember that these are abstracts we are counting, not people. It may be that the people who endorse AGW write far more articles than those who minimize it, or vice versa.

What I find interesting is how the great majority of abstracts (7,970 out of 11,944, or 67%) state no position on AGW. The next biggest group (24%) only implicitly endorse AGW. And that in an environment where "only idiots and crackpots" deny AGW. Could this be the case of the dog that didn't bark?

Since a worldwide rise in temperatures is, uncontroversially, a serious concern...

Let me concur with others: This is exactly the leap in the general public's impression that Cook, et al., are counting on, and it is absolutely a non sequitur.

"Serious concern" does not mean "is interesting and worth accepting a salary to study". "Serious concern" means "demands government action now to forestall". There is no doubt that the single actual measurable -- atmospheric CO2 -- is increasing. What is in question is whether it is something humanity should expend considerable wealth to prevent.

You write, "If that's all evidence does then it's useless, because it's supposed to support or contradict theories, explanations, or hypotheses which, naturally, go beyond the evidence itself."

The evidence in this case was to contradict the theory that only 1.6% of climate scientists agree that humans are the main cause of global warming. But that's all the evidence does.

"Since a worldwide rise in temperatures is, uncontroversially, a serious concern, whatever its cause and whatever the appropriate response, then the very acknowledgment of such a phenomenon is prima facie evidence of serious concern."

Seriously? OK, here are a couple of questions. As well as a "yes" or "no," I'd like you to explain your answers:

1) According to NASA GISTEMP, the global surface temperature rose by about 0.36 degrees Celsius from the decade of 1900-1909 to the decade of 1940-1949. *If* the that warming was entirely natural, would that be "uncontroversially, a serious concern"?

2) Per work of Richard Tol, a survey of economists indicates that the impact of global warming is likely to be a net positive to the GDP up to a temperature increase of 1 degree Celsius above approximately the present temperature.

MikeP says "There is no doubt that the single actual measurable -- atmospheric CO2 -- is increasing. "

Correct. That is the answer to a scientific question that is susceptible to careful measurement.

"What is in question is whether it is something humanity should expend considerable wealth to prevent."

(Or, try to prevent.) Either way, also correct.

This however is a question of what to do and what to spend and therefore is political not simply scientific.

I think it's a mistake to try to answer any political question as serious as this one, with science alone. Especially when the science has been marred by scandals over collecting and interpreting the data; by the yet-unexplained 15-year "pause" in what the temperature models had predicted; and by an unimpressive if not incompetent job of explaining it all to the public. Public support is crucial because the question of what to do and what to spend is political.

Also IMO, it's important to resolve this apparent inconsistency: (1) earth's four previous ice ages clearly did not end because of humans yet (2) the end of the present ice age is claimed to be mainly or even wholly because of humans - - even though its end actually began tens of thousands of years ago - - which I'm pretty sure was before the industrial age.

@Dana Nuccitelli,This argument is wrong and has been debunked several times, i.e. here and here.
Actually, I read both of the linked articles and they do not debunk the argument. Indeed, that would be hard to do since the argument is squarely based on Cook’s own data.

This argument is wrong and has been debunked several times, i.e. here and here.

Dana, you can not possibly "debunk" David Friedman's argument. It is irrefutably true.

John Cook, in his paper titled, "Agnotology, Scientific Consensus, and the Teaching and Learning of Climate Change: A Response to Legates, Soon and Briggs" made the following claim (on page 6): "Of the 4,014 abstracts that expressed a position on the issue of human-induced climate change, Cook et al. (2013) found that over 97% endorsed the view that the Earth is warming up and human emissions of greenhouse gases are the main cause." (Emphasis added.)

That is unquestionably a misrepresentation the Cook et al. (2013) paper, "Quantifying the consensus on anthropogenic global warming in the scientific literature," because only Level 1 endorsement ("Explicit endorsement with quantification") meets the criterion of stating that human emissions are the main cause. And only 62 abstracts (out of more than 3900) fell into that category.

No matter how much you and John Cook misrepresent your paper, that fact won't change. The appropriate thing to do, if you and John Cook actually cared about science--which it's pretty clear you don't--would be to acknowledge David Friedman's criticism as being correct, and change the paper titled, "Agnotology, Scientific Consensus, and the Teaching and Learning..."

Oh, and then you could go all through the Internet and try to correct your misrepresentations:

Question: Does this paper support the theory that global warming exists and is >50% human-inducted, oppose it, (or express no opinion)?

Support: 3,966
Oppose: 74

98% of papers which take a position endorse anthrogenic global warming.

(No Opinion: 7,970 - no information can be inferred from this, for the same reason that no information can be inferred about an labor economics paper's position on raising the minimum wage if the paper is about labor markets or even low-skill labor markets, but not directly about the minimum wage. Most papers on any topic in any discipline, are about Something Else than the particular aspect of the topic you think is the central issue of our time. Doesn't mean the economist in question endorses, or opposes a minimum wage. To me, that fully a third of the papers in the sample bothered to explicitly or implicitly take a side in this debate in the abstract (not even the text - the abstract), and that 98% of THOSE chose one side, is very strong evidence in favor of that side in a science. We aren't talking about X Studies in the humanities, where every paper has to establish its X studies political bona fides up front, we are talking about a science. If you believe otherwise, NO evidence is actually going to convince you, as you are beyond reason, wandering in the realms of metaphysics and faith.)

Even granting that AGW is a fact, it does NOT follow that it is "worrisome" or that gummint action is called for.

I am childfree by choice and I resent the implication that I should pay now or change my lifestyle in order to secure the future of the breeders' progeny. AGW is not at all worrisome to me, and those folks who find it worrisome should foot the bill for what it costs to fight AGW.

It is a fact that support for Windows XP is waning and is anthropogenic. That might well worry a lot of folks, namely those who insist on continuing to use XP, but nobody would suggest that we need gummint action to support XP, particularly at great cost and interference with the lifestyle of the general public.

It seems to an interested amateur that all of the posts belong to those from the same club. It might be interesting and informative to get the response of the scientists in question, or, at least, those who support their views - perhaps they aren't aware of this site. In the interests of free debate, perhaps you might include them in your discussion, unless y'all are happy just preaching to the converted.

Blogging software: Powered by Movable Type 4.2.1.
Pictures courtesy of the authors.
All opinions expressed on EconLog reflect those of the author or individual commenters, and do
not necessarily represent the views or positions of the Library of
Economics and Liberty (Econlib) website or its owner, Liberty Fund,
Inc.

The cuneiform inscription in the Liberty Fund logo is the
earliest-known written appearance of the word
"freedom" (amagi), or "liberty." It
is taken from a clay document written about 2300 B.C. in the Sumerian city-state of Lagash.